What version you use ? If you use the last (1.68), it display errors... when you click on the connect button... A lot of people have port problem ? Which port have you chosen (some of them are forbidden by firefox like the 21) ? Are you in http or https ?
______________________________________________
I understand your problem... I think you have'nt validate your settings... Effectively, the button connect is not active if your settings are not saved...
When your fill the fields for IP, port etc, you must validate it by clicking on the blue "V" button which appear at the right side of the field.
______________________________________________
The only case when the connection button always ride on ***Connection un progress*** (yes i made a typing error) is when you recieve a response but with a non good format... It mean that whether the problem is on the domain name or in the port... In your case i think they are good... (it is not a problem the port is redundant because it need to be here for technical reasons... but maybe your real acces port is not 443... i don't think so in your case but still check your port redirection settings on your NAS, try the 5001). Otherwise, i think the problem came from the type of account you have... I explain, if when you type your domain name "https://mydomain.com:443" in adress bar and it leads to a download station tab without access to anything else... It could be a probleme because my extension does not only use the Download Station API, and need an acces to the Authentification API... normaly it work even with a restrained account to Download Station but i don't know why, in some case, it fail...
Or maybe it is just simply a permission problem... in your settings panel on your NAS, check if your user account has acces to Download Station... Control Panel -> User -> select your account -> modify -> Applications tab (maybe in english it is not applications, maybe app or something like that) -> look if Download Station is checked and maybe DSM (not necessary normaly but maybe)...
__________________________________________________________________________
I don't think your problem come from login or password because if it was, an error should be displayed...
If you can type this on your firefox adress bar : https://YOURHOST:PORT/webapi/query.cgi?api=SYNO.API.Info&version=1&method=query&query=all
replace "YOURHOST" and "PORT" by yours and say me what is the response displayed on firefox.
It is a request of pre-connection, if you have a response, it could help me to identify the problem.
___________________________________________________________________________
OK, if you recieve a response by typing https://myNAS:5001/webapi........ in your address bar it mean that you sould use your "MyNAS" in the IP field and your "5001" in the port field and dont forget to check https (is in blue when is checked)... and normally it cannot be failed even if there is a problem whith login or password... it could't stay on "connection in progress" more than 5 second and after it display the type of error...
The only solution that i can see is maybe you havent checked the HTTPS field...
Otherwise if you have a little time to help me to relsove this problem, i can giving you instructions to check functions but it would be more easy by mail...
_____________________________________________________________________________________________
Sorry i could'nt answer you those days... I've seen your email, i've sent you one with a procedure to check your connection.